Magnetron



T. W. C. FISHER MAGNETRON Nov. 11, 1952 Filed May 2, 1951 Inventor Thomas W.C.Fisher-, by M 0% His Attorney Patented Nov. 11, 1952 MAGNETRON Thomas W. 0. Fisher, Rugby, England, assignor to General Electric Company, a corporation of New York Application May 2, 1951, Serial No. 224,096 In Great Britain August 17, 1950 4 Claims.

This invention relates to magnetrons of the multicavity type and, more particularly, to the construction of such-magnetrons in which magnetic pole pieces are enclosed in the evacuated envelope of the devices.

In the forming of a desirable electron discharge device of the magnetron type which employs an anode having resonant cavities therein, it is essential that thespacing of the anode, cathode, and pole pieces be accurately determined in a positive and simple way without tedious adjustments and that the accurate spacing be maintained during operation of the device. Further, it has been a problem in the past to make the final welded seals on the metal envelope of a magnetron without the deposition of contaminating products from the welding process upon electrodes therein, such products adulterating the previously carefully cleaned or coated surfaces of the electrodes and impairing properelectrical operation of the magnetron.

. It is, therefore, an object of the present invention to provide a new and improved structure for magnetrons of the multicavity type.

It is a second object of this invention to provide a magnetron of the type having enclosed pole pieces in which accurate spacing of the electrodes and pole pieces is easily effected by the particular construction of the various components.

It is a third object of this invention to provide a magnetron of the type having enclosed pole pieces for which the possibility of contamination of the electrode surfaces during the formation of the envelope is substantially eliminatedi;

In carrying out the objects of this invention, a tubularganode cylinder is provided and an axially shorter anode block, having resonant slots and cavities therein, is formed integrally or secured within the anode cylinder intermediate its opposite ends. Cylindrical pole pieces having outer diameters substantially the same as the inner diameter of the anode cylinder are inserted in the ends of the anode cylinder, being properly centered thereby, and secured therein by sleeves welded atone end of the anode cylinder and at the other end to the. pole pieces at points axially removed from the anode cylinder. The welded seals between the sleeves and the pole pieces are the last to be made during the formation of the envelope, and their remoteness from the region of the electrode surfaces substantially eliminates the possibility of chemical reaction or contaminating deposits on the surfaces from gaseous products of the welding process. Preferably, the

2 pole pieces are provided with shoulders there! around which abut with the ends ofithe anode cylinder to positively position the pole pieces in an axial direction. .Axial passagewaysare dentrally bored one each through the pole'pieces, through one of which a cathode structure extends, being supported in insulated relation from the pole piece. and through the other of. which a tuning member may be extended, being supported directly from the pole piece.

The novel features of this invention are pointed out with particularity in the appended claims. However, for a better understanding ofthe invention, together with further objects and ad vantages thereof, reference should be hadto the following description taken in conjunction with the accompanying drawing in which: r

Fig. 1 is an elevational view in section of a magnetron constructed in accordance with the present invention; Fig. 2 is a sectional view taken along line 2- -2 of Fig. 1; Fig. 3 isa plan view of the output chamber of the magnetron; and Fig, 4 is a sectional view taken along 4-4 in Fig. 1 to show the coupling connection be-, tween the resonant cavities and the output chamber.

Referring now to the drawing, there is shown a multicavity magnetron embodying the features of this invention and including a generally hollow tubular member or anode cylinder I. within which there is provided an anode block 2 defining a central opening therethrough around which a plurality of openings such as slots} and cavities 4,- resonant at some predetermined'frequency of operation, are symmetrically located- Anode block 2 is considerably shorter inaxial length than cylinder I and may be an integral part of cylinder l or a separate component, bonded within cylinder I intermediate its opposite ends. Both cylinder l and block 2 are preferably made of copper, which is easily machined and highly electrically and thermally conductive.

Two cylindrical magnetic pole pieces 5 and 6 are inserted into the opposite ends of cylinder I. Pole pieces 5 and 6 are generally similar in construction having nose portions 1 and 8 and head portions 9 and [0 respectively. The outerdiameters of nose portions 1 and 8, which extend into cylinder l, are approximately the same a-s-the inner diameter of cylinder I, so that the inner ends of the pole pieces are centered with respect to block 2 by the close fit. v Preferably shoulders I l and I2 are machined on nose portions land 8? respectively to abut against the ends of cylinder 1 and positively locate the inner ends of the pole.

sealed at the axially inner and smaller rims.

thereof to opposite ends of cylinder I. To accomplish this sealing, the smaller rims of sleeves l5 and I6 are inserted into circumferential grooves l1 and I8 in opposite ends of cylinder and sealed, preferably by brazing with a silvercopper eutectic alloy in an atmosphere of hydrogen. In order to insure that when the anode cylinder cools from the brazing temperature, the seal is not faulted as a result of the difference in thermal expansions of cylinder l, which is preferably copper, andthe sle. eve :s l5 and I6, which are-'preferably'steeI, the smallr rims of the sleeve are made thin in $9 55 section having athi'ckness in the order of 0.010 to :015", thus providingfthe rims with flexibility" and allowing them t' distort so. that cracks are prevented from forming in the brazing material. 1

The outer and larger rim portions of sleeves i and I6 are essentially the-same diameter'as head portions 9- and" 10150, that seals may be formed therebetween' to "enclose andfirmly-secure pole pieces 5-and 6 within "cylinder l as shown. These seals, as will be explained hereinafter, may be the last of'the envelope seals 'to' be 'made so that prior to their-effection the electrode surfaces'may be carefully cleaned, and then the seals made with little danger of contaminating the electrode surfaces since'theyarev remotely located, from the active electrode surfaces. "Il'rr'oi'igli passageway I5 there is extendeda cathode structure l9 which is supported'in insulated'andsealed relation from pole piece 5 by means of asiipport cylinder I 2 0, preferably made ofan '-'i1"on'-n-ickel'-cobalt alloy, secured at one end td-the wall-of a recess 2| in the outer face of pole piece 5 "and sealed at its other end to a glass insulator 22. Glass insulator 22, in turn, is 'sealed to 'a cap 23 which is bondedto the cathodestr'ucture 1-9 asshow-n. An emitting portion- [96 of cathode structure 9, coated with a nickel goxid'e :matrix or other suitable-emitting material, is positioned within anode block 2, centrally located therefrom. If it is desired that the magnetron be "adjustable o'r tunable in the frequency of operation, passageway- M mayb'e provided as shown; otherwise, pole piece 6' may be solid in construction. In this preferred embodiment, a tuning member 24is'supported by aspindle 25 extending through passageway M, spindle 25in turn being mounted on a flexible 'diaphragm 2-6 which is bonded in sealing relationship to a shoulder 27 in a recess 28 'formedin the outer face of pole piece 6 Axial movement of member 24 toward or away from black -2 to change the resonant frequency of slots 3 and cavities 4 1s afforded by means or an adjusting'scr'ew thread'formed on a sleeve 29'. attached 'to diaphragm 25- and spindle 25 as shown, thethread' cooperating with another threaded member; not shown, rotatably mounted in astructure secured to either sleeve it or pole piece 6.

Output means for the magnetron may be provided as shown, one side 30 of anode cylinder being flattened and bored to receive a coupling member 31, a cross section of which is shown by Fig. 4; Anode block 2 'is similarly provided 4 with a flattened side 32 to enable the end of coupling member 3| to project through flattened side 30 of cylinder and abut against aflattened surface of block 2. Coupling member 3| con" tains a dumb-bell shaped aperture therethrough defining, a slot 33 which is positioned to be in alignment. with an entrance slot 34 through wall 32 into the adjacent cavity 4 as shown by Fig. 2. Coupling member 3| thus provides communication between the interior of anode block 2 and an output chamber 35, which is preferably made of an ironnickel-cobalt alloy in order that a glass window BB- may be sealed therein. In the arrangement .illustrated, chamber 35 is rectangular in cross section so that it may be joined to a rectangularwave guide, not shown, taking the high-frequency oscillatory output from the magnetron.

' If necessary, tuning member 24, which is in the form of a flanged substantially cylindrical disk having a rimprojecting toward the ends of cavities-"4, 'maybe flattened somewhat onone side asshow-n in order that itclears coupling member 3| in axial" movement. An" exhaust tubulation 31 may conveniently beprovided through the wallet-cylinder |'-as*show-n;

'When a voltage making the anode-block; 2 positive in potential'with'l respect to the cathode struc-'- ture- |9- is applied between the two electrodes creating a radial electric field-therebetween, and an axial magnetiefield-is established in the interelec'trodespace by magnetic flux passing through the pole pieces '5 and 6-, electrons emitted by cathode portion-|9a-, which i's'he'ated', travel in curvilinear paths toward the anodeblock' 2 in such a manner as to set uphigh frequency electric and; magnetic-field-oscillationswithinslots 3 and cavities-'4. 'The frequency of the oscilla tions is dependentupon the space' resonant con figuration of slots '3'a-nd; cavities 4, and maybe varied considerably by-aia axial movement of tuningmemb'er'Zl whichvaries-the capacitive-inductive relationship of slots-3 and cavities 4. High frequency energy is extracted from the oscillatingwfield's in anode block 2 through coupling member 31 an'doutput chamber 35'. Such electrical operation of the magnetron is wellv known to those skilled in the art andjit'is not the purpose of the present invention to provide a magnetron having unique electrical operation bizti'to provide. a magnetronhaving new and advantageous structural features.

In assembling the magnetron parts, the anode cylinder and anode block. 'Z -are first brazed-together or formed as one piece. Cup-shaped sleeves |-5 and lfi are-next bonded in" grooves H and I2 b 'the preferred method'given hereinbefore; and coupling member 3|, output chamber 3:5, and exhaust tribulation 3-! are brazed in place. Support cylinder 20and cap 23 are sealed axially by shoulder bearin on the upper end of cylinder Cathode structure -|9 is next iii-- serted through passageway |'3 in pole piece 5 until the emitting portion |9d is positioned with-' in the central opening-of anode block 2. An accurately centered jig} preferably in two or mor e sections, is slipped up into the central opening ofanode block 2 to center the emitting portion l9a in radial position, after which the bond at 38 is made between cap 23 and cathode structure 19. The bond at 38 is thus made in the manner which assures that emitting portion l9a is properly centered when the magnetron is completely assembled.

Following the bonding at 38, pole piece 5 with cathode structure [9 attached thereto is withdrawn from anode cylinder l, the jig removed from the central opening in anode block 2 and poleflpiece 5 re-inserted into cylinder I after the final inspection and cleaning of the active electrode surfaces is made. The seal between the larger rim of sleeve l5 and pole piece 5 ismade byjbonding or welding sleeve l5 to a sealing collar 39, which is previously bonded to pole piece 5. This bond between sleeve l5 and collar 39, it will be noted, being one of the two final bonds to be made and being far removed from the re-- gi'o'nof anode block 2 and emitting portion [9a, presents no danger that the cleaned electrode surfaces will be adulterated by chemical reaction or contaminating deposits on the active electrode surfaces from gaseous products of the bond- 1 ing process.

Before pole piece 6 is inserted into cylinder I, spindle carrying diaphragm 26 is inserted through passageway M. The narrowed portion of passageway I4 in nose portion 8 centers spindle 25 while diaphragm 26 is weldedto pole piece 6. Tuning member 24 is then attached to the end of spindle 25, and pole piece 6 inserted into anode cylinder I. Again, nose portion 8 is positioned radially by its snug fit with cylinder 1 and axially by shoulder l2 bearing upon the end of cylinder l. The other final welded seal is then similarly made by bonding or Welding a collar 40, previou'sly attached to pole piece 6, to the larger rim will be understood, of course, that some external return path, not shown, for the magnetic flux to be carried by pole pieces 5 and 6 is to be provided during operation of the device. Such a return path may be either of the nature of soft iron if pole pieces 5 and 6 are permanently mag netized, or may contain a source of magnetomothis force for driving flux through pole pieces 5 and 6 and across the interelectrode space, if the pole pieces are not permanently magnetized.

"It will be apparent that anode cylinder I may be made in the form of a tubular anode mem-' ber having a rectangular, oval, or other geometric cross section different from the circular cross section of cylinder l, the nose portions 7 and 8 being similar in size and cross sectional geometry as the opening through the tubular member. Further, the cross sectional shapes of head portions 9 and I0 need not be circular as long as the outer rims of sleeves l5 and I 6 are shaped similarly or so that they may be bonded to the. head portions.

-While the present invention has been described by, reference to a particular embodiment thereof,

it. will be understood that numerous modifications may be made by those skilled in the artwithout actually departing from the invention. It therefore, intended by the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What is claimed in desire to secure by Patentof the United States is:

1. A magnetron of the multicavity type comprising a generally hollow tubular anode member having an anode block portion therein inter--' mediate the ends thereof, said anode block portion defining a central opening therethrough; and a plurality of resonant cavities around said central opening, two pole pieces having nose portions and head portions, said nose portions being similar in size and cross section to the axial opening defined by said tubular anode member and being centered within opposite ends of said tubular anode member, connecting sleeves bonded to said anode member and at the opposite end to said head portions, the bonds of said sleeves to said head portions being at points axially remote from said anode block portion so that said head portions are encircled by said sleeves, a central axial passageway through one of said pole pieces, a cathode structure extending through said passageway into the region of said resonant cavities, and means supporting said cathode structure in insulated and sealed relation from said one pole piece.

2. A magnetron of the multicavity type comprising an anode cylinder having resonant cavities defined therein intermediate its ends, two cylindrical pole pieces having nose portions inserted into the opposite ends of said anode cylinder and being centered thereby and head portions extending axially from said anode cylinder, sleeves bonded to the ends of said anode cylinder and additional sleeves bonded to the ends of said head portions axially remote from said anode cylinder to retain said pole pieces in said anode cylinder, said sleeves bein bonded together at their outer ends, an axial passageway through one of said pole pieces, a cathode structure extending through said passageway into the region of said resonant cavities, and means supporting said cathode structure in insulated and sealed relation from said one pole piece.

3. A multicavity magnetron comprising an anode cylinder; an anode block of smaller axial length than said anode cylinder secured within said anode cylinder intermediate its opposite ends; two cylindrical pole pieces each having a nose portion, a head portion, and a shoulder around said nose portion; said nose portions positioned within the opposite ends of said anode cylinder and centered thereby with respect to said anode block, said shoulders abutting against the opposite ends of said anode cylinder to axially position said pole pieces with respect to said anode block, and said head portions extending axially from said anode cylinder; connecting sleeves hermetically sealed between the ends of said anode cylinder and said head portions of said pole pieces at points remote from said anode cylinder to complete an hermetically sealed envelope formed by said anode cylinder and said pole pieces; a centrally located axially extending passageway through one. of said pole pieces, a cathode structure extending through said passageway to the region of said anode block; and means supporting said cathode structure in insulated and hermetically sealed relation from said one pole piece.

4. A multicavity magnetron comprising a generally hollow anode cylinder; an anode block axially shorter than said anode cylinder positioned within said anode cylinder intermediate its two ends and defining a central opening with resonant cavities therearound; two cylindrical Letters 27 polea pieces z each having a noseportion of diameter approximately thesame as the inner diam,- eter. or; said anode cylinder, a headportion of diameter greater than that of said nose portion, and a shoulder therearound; between said nose and said head portion;o,said nose portions extending axially into the opposite ends of said anode cylinder and being centered thereby with respect to said anode block, said shoulders abutting-against the opposite ends of said anode cyl- 'inder to position said nose portions axially with respect to said anode block, and said head portions-extending axially from said anode cylinder; two .cup-like sleeves having the smaller rims thereof hermetically bonded to the opposite ends ofsaid anode cylinder, and the larger rims thereofhermetically bonded to the axially remote ends ofsaid head portions; a centrally bored axially extending passageway through one of said pole pieces;- a cathode structure. extending through said passageway into the region of said resonant cavities; and means.v supporting said cathode structure in insulated and hermetically sealed relation from said one pole piece.

W. 'C. FISHER. 1

REFERENCES CITED The following references are of record in the file of this patent:

STATES PATENTS Number. Name Date 2,406,276 White Aug. .20, 1946 2,466,922 Wax Apr. 12, 1.949 2,478,53 Kather- Aug.v 9, 1949 2,542,899 Brown Feb. 20, .1951 2,557,780 Brown June 19, .1951 2,567,624 Thomson et a1. Sept. 11, 1951 FOREIGN PATENTS Number Country, Date Great Britain July -11, 1939 

